Package having substrate with embedded metal trace overlapped by landing pad

ABSTRACT

An embodiment package includes a conductive pillar mounted on an integrated circuit chip, the conductive pillar having a stepper shape, a metal trace partially embedded in a substrate, the metal trace having a bonding pad portion protruding from the substrate, and a solder feature electrically coupling the conductive pillar to the bonding pad portion of the metal trace.

BACKGROUND

In a package such as a flip chip Chip Scale Package (fcCSP), anintegrated circuit (IC) may be mounted to a substrate (e.g., a printedcircuit board (PCB) or other integrated circuit carrier) through a bumpon trace (BOT) interconnection.

In light of the demand for ever smaller packages, attempts are oftenmade to reduce the distance between adjacent bumps, which is known asthe bump pitch. One way to reduce the bump pitch is by shrinking thewidth of the metal traces used in the BOT interconnection.Unfortunately, reducing the width of the metal traces may lead toundesirable or detrimental consequences.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross section of an embodiment package having astepper-shaped conductive pillar and a partially embedded metal traceproviding a protruding bonding pad portion;

FIGS. 1A-1B illustrate a cross section of conventional probe testingconfigurations;

FIG. 1C illustrates a cross section of an embodiment probe testingconfiguration;

FIG. 2 illustrates a cross section of an embodiment package having astepper-shaped conductive pillar and a partially embedded metal traceproviding a stepper-shaped protruding bonding pad portion;

FIG. 3 illustrates a cross section of an embodiment package having astepper-shaped conductive pillar and a partially embedded metal traceproviding an inverted stepper-shaped protruding bonding pad portion;

FIG. 4 illustrates an embodiment package with a partially embedded metaltrace providing a longer protruding bonding pad portion;

FIG. 5 illustrates an embodiment package with a partially embedded metaltrace providing an even longer protruding bonding pad portion;

FIGS. 6A-6F collectively schematically illustrate a process of formingthe embodiment packages of FIGS. 1-3;

FIGS. 7A-7F collectively schematically illustrate a process of formingthe embodiment packages of FIGS. 4-5;

FIGS. 8A-8B illustrate a cross section of conventional packages; and

FIG. 8C illustrates a cross section of an embodiment package using bothprojecting and embedded traces.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the disclosure providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, namely a package incorporating a bump on trace (BOT)interconnection. The concepts in the disclosure may also apply, however,to other packages, interconnection assemblies, or semiconductorstructures.

Referring now to FIG. 1, an embodiment package 10 is illustrated. Aswill be more fully explained below, the geometry of the conductivepillar 12 prevents or inhibits delamination of the conductive pillar 12from the dielectric layer within the device layer 14 of the integratedcircuit chip 16 due to, for example, a coefficient of thermal expansion(CTE) mismatch between the chip 16 and the substrate 18.

In addition, the geometry of the bonding pad portion 20 of the metaltrace 22 inhibits or prevents undesirable bridging of the solder feature24 between adjacent traces, cold joining between the conductive pillar12 and the metal trace 22, and peeling of the metal trace 22 from thesubstrate 18.

The configuration of the conductive pillar 12 and/or the metal trace 22in FIG. 1 also ensures a sufficient stand-off distance between theintegrated circuit chip 16 and the substrate 18 for the introduction ofunderfill or molding compound 26 as the bump pitch shrinks. Theconfiguration of also provides enough space to permit testing of thebump-on-trace connection using, for example, probes or other testingequipment. Indeed, as shown in FIGS. 1A-1B, testing difficulties may beexperienced in conventional testing configurations. In FIG. 1A, a falsealarm indicating a short may be triggered when the probe pininadvertently contacts the bonding pad portion 20 of both an intendedtrace 22 and an adjacent neighboring trace 22 if the bonding padportions 20 of the traces 22 project above the top surface of thesubstrate 18. In FIG. 1B, it may be difficult for the probe pin tocontact the traces 22 when all of the traces 22 are embedded in thesubstrate 18. In contrast, as shown in FIG. 1C, when the configurationof the traces 22 alternates such that one trace 22 includes a projectingbonding pad portion 20 and a neighboring trace 22 is embedded in thesubstrate 18 the difficulties or problems associated with FIGS. 1A-1Bare overcome. In other words, using the orientation of FIG. 1C, theprobing pitch is at least doubled.

As shown in FIG. 1, the embodiment package 10 includes the integratedcircuit (IC) chip 16 (a.k.a., a die). In an embodiment, the integratedcircuit chip 16 includes one or more device layers 14 with a dielectricmaterial. The dielectric material may be, for example, an extremelylow-k (ELK) dielectric. As used herein, ELK refers to a dielectricmaterial having a dielectric constant of about 2.5 or less, andpreferably between 1.9 and 2.5. The device layers 14 may include asingle layer of the dielectric material or several layers of thedielectric material.

A conductive pillar 12 is mounted to the underside of the integratedcircuit chip 16. In an embodiment, the conductive pillar 12 engages withor abuts against the dielectric material in the in the outermost devicelayer 14 of the integrated circuit chip 16. As shown, the conductivepillar 12 extends below or beneath the integrated circuit chip 16 afterthe chip has been flipped during the flip chip packaging process.

In an embodiment, the conductive pillar 12 has a stepper shape, whichresembles an inverted truncated cone. Therefore, a diameter or width ofthe conductive pillar 12 diminishes as the conductive pillar extendsaway from the integrated circuit chip 16 and toward the substrate 18. Inother words, the conductive pillar 12 tapers from bottom (near the IC16) to top (near the solder feature 24) as oriented in FIG. 1.

While the conductive pillar 12 in FIG. 1 is depicted as having a lineartaper, the conductive pillar 12 may have sidewalls that are curved,terraced, or otherwise configured and still be considered to have astepper shape. In an embodiment, the conductive pillar 12 is formed froma suitable material such as, for example, copper (Cu), nickel (Ni), gold(Au), palladium (Pd), titanium (Ti), or alloys thereof.

Still referring to FIG. 1, the embodiment package 10 also includes ametal trace 22. In an embodiment, the metal trace 22 is formed fromcopper (Cu), nickel (Ni), gold (Au), aluminum (Al), silver (Ag), oralloys thereof. In an embodiment, the metal trace 22 is coated with asurface treatment such as, for example, organic solderabilitypreservatives (OSP), immersion tin (IT), and so on.

The metal trace 22 is partially embedded in the substrate 18. Becausethe metal trace 22 is partially embedded, the metal trace 22 providesthe bonding pad portion 20. As shown, the bonding pad portion 20protrudes or projects from the underlying substrate 18. In other words,the bonding pad portion 20 is disposed above the top surface of thesubstrate 18 and is not encapsulated by the substrate 18.

In an embodiment, a top width a of the bonding pad portion 20 is equalto, or approximately equal to, a bottom width b of the bonding padportion 20. In an embodiment, a bottom width b of the bonding padportion 20 is greater than or equal to about 10 μm and less than orequal to about 25 μm. In an embodiment, a height h_(s) (a.k.a.,thickness) of the bonding pad portion 20 is greater than or equal toabout 1 μm and less than or equal to about 20 μm. In an embodiment, aheight h_(w), of the conductive pillar 12 is greater than or equal toabout 20 μm and less than about 50 μm.

The solder feature 24 (e.g., solder joint) electrically couples theconductive pillar 12 to the bonding pad portion 20 of the metal trace22. In an embodiment, the solder feature 24 is a solder ball, solderpaste, or another conductive component suitable for electricallycoupling devices together. In an embodiment, the solder feature 24 isformed from a material that can be reflowed to electrically bond thedevices together.

Referring now to FIG. 2, in an embodiment a bottom width b of thebonding pad portion 20 is greater than a top width a of the bonding padportion 20. In this configuration, the bonding pad portion 20 has astepper shape. In other words, a diameter of the bonding pad portion 20tapers from bottom to top (i.e., a periphery of the bonding pad portion20 gets smaller the farther away from the substrate 18 the bonding padportion 20 projects).

In an embodiment, the bonding pad portion 20 utilizes the stepper shapeshown in FIG. 2 the formula b−a>0.36h_(s)−0.1 μm is satisfied, where bis a bottom width of the bonding pad portion, a is a top width of thebonding pad portion, and h_(s) is a height of the bonding pad portion.

Referring now to FIG. 3, in an embodiment a top width a of the bondingpad portion 20 is greater than a bottom width b of the bonding padportion 20. In this configuration, the bonding pad portion 20 has aninverted stepper shape. Indeed, a diameter of the bonding pad portion 20tapers from top to bottom. In other words, a diameter of the bonding padportion 20 tapers from top to bottom (i.e., a periphery of the bondingpad portion 20 gets larger the farther away from the substrate 18 thebonding pad portion 20 projects).

In an embodiment, the bonding pad portion 20 utilizes an invertedstepper shape as shown in FIG. 3 when a formula a−b>0.36h_(s)−0.1 μm issatisfied, where a is a top width of the bonding pad portion, b is abottom width of the bonding pad portion, and h_(s) is a height of thebonding pad portion.

With regard to FIGS. 4-5, it was discovered that the height h_(w) of theconductive pillar 12 had an effect on the ELK stress. Indeed, as theheight h_(w) of the conductive pillar 12 was reduced, the pillardimension d became larger. Therefore, when the coefficient of thermalexpansion (CTE) mismatch occurred, the solder feature 24 deformed toabsorb a portion of the force. With a larger pillar dimension d, theamount of deformation is reduced at the sides of the conductive pillar12 and increased at the sides of the protrusion bonding pad portion 20,which yielded a smaller stress to the ELK.

Unfortunately, the reduction in the height h_(w) of the conductivepillar 12 noted above may reduce the stand-off height (i.e., thedistance between the integrated circuit chip 16 and the substrate 18).When the stand-off height is reduced too much, the introduction ofunderfill or molding compound in that area may be negatively affected.For example, because of the small stand-off dimension voids may occur.Thus, there is the potential for failure of the device and reliabilityis diminished.

To resolve this issue experienced when the height h_(w) of theconductive pillar 12 is reduced, a longer bonding pad portion 20 isproposed. As will be more fully explained below, the taller or thickerbonding pad portion 20 of the metal trace 22 maintains a sufficientstand-off dimension to ensure suitable and smooth flow of the underfillmaterial or molding compound.

As shown in FIGS. 4-5, in an embodiment the height h_(s) of the bondingpad portion 20 of the metal trace 22 is increased relative to the h_(s)of the bonding pad portion 20 in some other embodiments. For example,the height h_(s) of the bonding pad portion 20 may be greater than orequal to the height of the conductive pillar 12.

As shown in FIG. 4, in an embodiment the height h_(w) of the conductivepillar 12 is greater than or equal to about 10 μm and less than or equalto about 30 μm when the height h_(s) of the bonding pad portion 20 isgreater than or equal to about 20 μm and less than or equal to about 40μm.

As shown in FIG. 5, in an embodiment the height h_(w) of the conductivepillar 12 is greater than or equal to about 1 μm and less than or equalto about 10 μm when the height h_(s) of the bonding pad portion 20 isgreater than or equal to about 20 μm and less than or equal to about 40μm.

FIGS. 6A-6F collectively schematically illustrate a process of formingthe embodiment packages 10 of FIGS. 1-3. In FIG. 6A, a coreless build upprocess is implemented using a carrier 28. As shown, during the corelessbuild up process a metal material 30 (e.g., copper, etc.) is introducedinto openings in the substrate 18 for the purpose of forming each metaltrace 22.

Once the metal material 30 has been suitably formed within the substrate18, the protrusion pad structure 32 is separated or released from thecarrier 28 as shown in FIG. 6B. Thereafter, in FIG. 6C, a photo resist(PR) 34 is formed over the metal material 30 and patterned. In anembodiment, the angle of the sidewalls of the photo resist 34(highlighted by dashed lines and an arrow) is controlled by tuning theexposure and developing parameters during the photolithography process.

After the photo resist 34 has been patterned, a metal plating (e.g.,copper plating) process is performed as shown in FIG. 6D. The platingprocess is performed to deposit or introduce the metal material 30 intothe openings in the patterned photo resist 34. Once the photo resist 34has been removed as shown in FIG. 6E, a metal etching process isperformed to remove portions of the metal material 30 between thebonding pad portions 20 of the adjacent metal traces 22.

In the embodiment of FIG. 6E, the bonding pad portion 20 of the metaltrace 22 has a stepper shape. In other words, the bonding pad portion 20has a diminishing diameter as the bonding pad portion 20 projects awayfrom the substrate 18.

As shown in FIG. 6F, a solder resist coating 36 may be formed overportions of the substrate 18 prior to the bonding pad portion 20 of themetal trace 22 being used to form an electrical connection within thepackage 10. It should be recognized that additional processes may beperformed during the fabrication of the package 10 of FIGS. 1-5 inpractical applications.

FIGS. 7A-7F collectively schematically illustrate a process of formingthe embodiment packages of FIGS. 4-5. In FIG. 7A, the coreless build upprocess is implemented using the carrier 28. As shown, during thecoreless build up process the metal material 30 (e.g., copper, etc.) isintroduced into openings in the substrate 18 for the purpose of formingthe metal trace 22.

Once the metal material 30 has been suitably formed within the substrate18, the protrusion pad structure 32 is separated or released from thecarrier 28 as shown in FIG. 7B. Thereafter, in FIG. 7C, a photo resist(PR) 34 is formed over the metal material 30 and patterned. In anembodiment, the thickness of the photo resist 34 in FIG. 7C is muchgreater than, for example, the thickness of the photo resist 34 in FIG.6C. In addition, in an embodiment the sidewalls of the photo resist 34are vertically-oriented (i.e., make a right angle with the top surfaceof the metal material 30).

After the photo resist 34 has been patterned, a metal plating (e.g.,copper plating) process is performed as shown in FIG. 7D. The platingprocess is performed to deposit or introduce the metal material 30 intothe openings in the patterned photo resist 34. Once the photo resist 34has been removed as shown in FIG. 7E, a metal etching process isperformed to remove portions of the metal material 30 between thebonding pad portions 20 of the adjacent metal traces 22.

In the embodiment of FIG. 7E, the bonding pad portion 20 of the metaltrace 22 has a rectangular shape. In other words, the bonding padportion 20 has a relatively constant diameter as the bonding pad portion20 projects away from the substrate 18. In addition, the bonding padportion 20 in FIG. 7E is substantially taller (or thicker) than thebonding pad portion 20 depicted in FIG. 6E. Therefore, the bonding padportion 20 in FIG. 7E may be referred to as a long bonding pad portion20.

As shown in FIG. 6F, a solder resist coating 36 may be formed overportions of the substrate 18 prior to the bonding pad portion 20 of themetal trace 22 being used to form an electrical connection within thepackage 10. It should be recognized that additional processes may beperformed during the fabrication of the package 10 of FIGS. 1-5 inpractical applications.

From the foregoing it should be recognized that the embodiment packagesdisclosed herein provide advantageous benefits and features. Forexample, the geometry of the conductive pillar 12 prevents or inhibitsdelamination of the conductive pillar 12 from the extremely low-kdielectric layer of the chip 16 due to, for example, a coefficient ofthermal expansion (CTE) mismatch between the chip 16 and the substrate18. In addition, the geometry of the protruding bonding pad portion 20of the metal trace 22 inhibits or prevents undesirable bridging of thesolder feature 24 between adjacent traces, cold joining between theconductive pillar 12 and the metal trace 22, and peeling of the metaltrace 22 from the substrate 18.

As shown in FIG. 8A, in conventional configurations a short may occurdue to the small pitch between adjacent traces (represented by the arrowbetween the adjacent traces). As shown in FIG. 8B, in conventionalconfigurations an open circuit may occur unless the bump and the tracein the cavity of the substrate 18 are very accurately aligned. Incontrast, where the traces 22 alternate (e.g., one trace 22 projectsfrom the substrate 18 and the neighboring trace 22 is embedded in thesubstrate 18), both the short window and the open window are improved asshown in FIG. 8C. Indeed, where the passing line or trace 22 is recessedbetween the bump structures utilizing protruding traces 22 the assemblyprocess for the embodiment package 10 is improved.

An embodiment package includes a conductive pillar mounted on anintegrated circuit chip, the conductive pillar having a stepper shape, ametal trace partially embedded in a substrate, the metal trace having abonding pad portion protruding from the substrate, and a solder featureelectrically coupling the conductive pillar to the bonding pad portionof the metal trace.

An embodiment package includes a conductive pillar mounted on anintegrated circuit chip, the conductive pillar having a stepper shapeand defining a conductive pillar height, a metal trace partiallyembedded in a substrate, the metal trace having a bonding pad portionprotruding from the substrate, the bonding pad portion defining abonding pad portion height, the bonding pad portion height greater thanor equal to the conductive pillar height, and a solder featureelectrically coupling the conductive pillar to the bonding pad portionof the metal trace.

An embodiment method of forming a package includes mounting a conductivepillar having a stepper shape to an integrated circuit chip, partiallyembedding a metal trace in a substrate, the metal trace having a bondingpad portion protruding from the substrate, and electrically coupling theconductive pillar to the bonding pad portion of the metal trace.

While the disclosure provides illustrative embodiments, this descriptionis not intended to be construed in a limiting sense. Variousmodifications and combinations of the illustrative embodiments, as wellas other embodiments, will be apparent to persons skilled in the artupon reference to the description. It is therefore intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A package, comprising: a conductive pillarmounted on an integrated circuit chip, the conductive pillar having astepper shape; a metal trace partially embedded in a substrate, themetal trace having a bonding pad portion and a recessed portion, thebonding pad portion protruding from the substrate, the recessed portionhaving a top surface lower than an uppermost surface of the substratesuch that the substrate extends below the recessed portion and extendsabove the recessed portion, wherein an upper surface of the recessedportion is free of the substrate; and a solder feature electricallycoupling the conductive pillar to the bonding pad portion of the metaltrace.
 2. The package of claim 1, wherein the bonding pad portion has astepper shape.
 3. The package of claim 1, wherein the bonding padportion has an inverted stepper shape.
 4. The package of claim 1,wherein a diameter of the bonding pad portion tapers from top to bottom.5. The package of claim 1, wherein a diameter of the bonding pad portiontapers from bottom to top.
 6. The package of claim 1, wherein a topwidth of the bonding pad portion is less than a bottom width of thebonding pad portion.
 7. The package of claim 1, wherein a top width ofthe bonding pad portion is greater than a bottom width of the bondingpad portion.
 8. The package of claim 1, wherein the bonding pad portionutilizes a stepper shape when a formula b−a>0.36hs−0.1 μm is satisfied,where b is a bottom width of the bonding pad portion, a is a top widthof the bonding pad portion, and hs is a height of the bonding padportion.
 9. The package of claim 1, wherein the bonding pad portionutilizes an invertd stepper shape when a formula a−b>0.36hs−0.1 μm issatisfied, where a is a top width of the bonding pad portion, b is abottom width of the bonding pad portion, and hs is a height of thebonding pad portion.
 10. The package of claim 1, wherein a height of thebonding pad portion is greater than or equal to about 1 μm and less thanabout 20 μm when a height of the conductive pillar is greater than orequal to about 20 μm and less than about 50 μm.
 11. The package of claim1, wherein a bottom width of the bonding pad portion is greater than orequal to about 10 μm and less than or equal to about 25 μm.
 12. Thepackage of claim 1, wherein a height of the bonding pad portion isgreater than or equal to about 10 μm and less than or equal to about 20μm.
 13. A package, comprising: a conductive pillar mounted on anintegrated circuit chip, the conductive pillar having a stepper shapeand defining a conductive pillar height; a metal trace partiallyembedded in a substrate, the metal trace having a bonding pad portionprotruding from the substrate and a recessed portion recessed from anoutermost surface of the substrate, an entirety of the metal tracefacing the integrated circuit chip being free of the substrate, thebonding pad portion defining a bonding pad portion height, the bondingpad portion height greater than or equal to the conductive pillarheight; a solder feature electrically coupling the conductive pillar tothe bonding pad portion of the metal trace; a neighboring metal traceembedded in the substrate and adjacent to the metal trace, a top surfaceof a portion of the neighboring metal trace disposed beneath anuppermost surface of the substrate; and an underfill interposed betweenthe integrated circuit chip and the substrate, the underfill contactingsurfaces of the neighboring metal trace and the recessed portion. 14.The package of claim 13, wherein the conductive pillar height is greaterthan or equal to about 1 μm and less than or equal to about 10 μm whenthe bonding pad portion height is greater than or equal to about 20 μmand less than or equal to about 40 μm.
 15. The package of claim 13,wherein the conductive pillar height is greater than or equal to about10 μm and less than or equal to about 30 μm when the bonding pad portionheight is greater than or equal to about 20 μm and less than or equal toabout 40 μm.
 16. The package of claim 13, wherein the integrated circuitchip includes a device layer with an extremely low-k (ELK) dielectriclayer abutting the conductive pillar.
 17. The package of claim 13,wherein an underfill material is disposed around the conductive pillarand the bonding pad portion of the metal trace and between theintegrated circuit chip and the substrate.
 18. A method of forming apackage, comprising: mounting a conductive pillar having a stepper shapeto an integrated circuit chip; partially embedding a metal trace in asubstrate, the metal trace having a bonding pad portion protruding fromthe substrate and a recessed portion; partially embedding a neighboringmetal trace in the substance adjacent to the metal trace, a top surfaceof a portion of the neighboring metal trace closest to the bonding padportion being disposed beneath an uppermost surface of the substrate;and electrically coupling the conductive pillar to the bonding padportion of the metal trace, wherein a surface of the substrate is closerto the integrated circuit chip than a surface of the recessed portion,the surface of the recessed portion being free of the substrate.
 19. Themethod of claim 18, further comprising forming the bonding pad portionsuch that the bonding pad portion has a stepper shape.
 20. The method ofclaim 18, further comprising forming the bonding pad portion such thatthe bonding pad portion has an inverted stepper shape.